In the related art, there is a known fluorescence endoscope apparatus with which a fluorescence image and a reflected-light image of an observation subject are acquired by irradiating light in a wavelength band for exciting a fluorescent substance and light in a wavelength band for normal observation while switching between them by means of a rotating filter, and both images are observed with appropriate brightnesses (for example, see Patent Literature 1). With this fluorescence endoscope apparatus, the aperture and exposure time for a liquid crystal are changed depending on whether or not fluorescence observation is performed; image data that is imaged and signal converted by a CCD is multiplied by a preset coefficient; this is added to image data accumulated up to one frame immediately before it, which is stored in a frame memory; and the data is stored in the frame memory and is also output.